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Intake and digestibility trials were conducted with sheep to evaluate the effect of adding various levels of a typical fibrous grass forage (neutral detergent fiber, NDF=68%) to a high quality, low fiber (NDF=22%) brassica forage. Four forage rape:orchardgrass hay diets (0, 40, 70, 100% rape content on a dry matter basis) were fed to groups of six Polled-Dorset crossbred growing wether lambs (39.6 kg) individually housed in metabolism crates. After a 7-d ad libitum intake period, a 7-d digestibility trial was conducted at 90% of the observed ad libitum intake level. Digestible dry matter intake (DDMI) per unit metabolic body weight increased as rape in the diet was increased from 0 to 70%, with increases in both dry matter intake and dry matter digestibility (DMD). However, DDMI was similar for lambs fed the 70 and 100% rape diets, with DMI decreasing to the same relative extent as DMD increased. Digestibility of the cell wall fraction of the two intermediate diets (40% rape and 70% rape) was lower than predicted from component forage digestibilities. This observation suggests the existence of an associative effect similar to that often reported when forage and concentrates are fed in various ratios. Forage brassicas appear to be utilized in the ruminant in a manner more typically resembling a concentrate than a forage.

Experiments described were conducted to define the vitamin A status of ewes and lambs grazing orchardgrass fertilized at various levels of N or N plus micro-elements. Four fertilizer treatments (56 kg N/ha; 168 kg N/ha; 504 kg N/ha; 504 kg N/ha + Co, Cu, Mo, Zn and S) were applied to replicated hay and pasture plots of Potomac orchardgrass on a Gilpin silt loam soil. Ewe lambs were allocated randomly to fertilizer treatment groups and maintained on pasture and hay from 1967 to 1971.Forage nitrate and carotene levels increased with increasing levels of N fertilizer, but fertilizer level did not affect ewe blood carotene, blood vitamin A or liver vitamin A levels. Overall average values were .06% NO3-N and 127 mg carotene per kilogram of forage DM, 12.3 mcg carotene and 26.7 mcg vitamin A per 100 ml of blood, and 92.5 mcg vitamin A per gram of fresh liver.

Zinc concentrations in alfalfa hay were varied using a N-Zn liquid fertilizer as a foliar applicant (.34 or .68 kg Zn/ha) or as a soil fertilizer (4.07 kg Zn/ha). Mean concentrations of Zn across five cuttings of alfalfa in 2 yr were 18, 27, 41 and 21 mg Zn/kg DM for control, low foliar, high foliar and soil treatments, respectively. Each treatment was fed in ad libitum amounts to eight crossbred wether lambs (20 to 35 kg) in 6-wk growth and intake trials, followed by 2-wk digestibility and balance trials with individual lambs. For one cutting, hays were also fed in an 81-d trial to four ram lambs (30 to 35 kg) and live weight gain and testicular development were measured. Average daily gain (ADG) and intake over 6 wk differed (P<.01) with cutting but not with Zn treatment. Average daily gain and testes weight of ram lambs also were not affected by treatment. In the metabolism trials, Zn treatment did not alter (P>.05) intake or dry matter digestibility (DMD) of alfalfa, but did influence digestibility of neutral detergent fiber (NDF). Digestible NDF (%) was higher (P<.05) for high foliar than for low foliar treatments. Apparent absorption and retention of Zn was significantly greater for control than for Zn-treated alfalfas and did not differ with cutting. Mean serum Zn concentrations for control, low and high foliar, and soil treatments were .79, .81, .78 and .75 μg Zn/ml, respectively, for all cuttings, with no differences due to treatment. Results do not suggest an appreciable response in lamb growth or Zn status to increased levels of Zn in a forage diet containing a marginal level of the element.

Intake, digestibility and mineral balance trails were conducted with two warm-season grasses, switchgrass and big bluestem, harvested at different cutting dates in 2 yr. Switchgrass was grown in Pennsylvania, New York, New Jersey, Kentucky and Iowa, and big bluestem in Pennsylvania. The hays were fed ad libitum to mature beef cows and mature wether sheep and intake and digestibilities of dry matter, neutral detergent fiber (NDF) and protein were determined. Composition of the hays was characterized by high levels of NDF (67.6 to 83.8%) and relatively low concentrations of crude protein (4.8 to 13.6%) and certain elements (P, S, Zn). Dry matter, NDF and protein digestibility by cattle and sheep declined (P<.05) with advancing maturity of the grasses. Mean dry matter digestibility (DMD) by beef cows decreased from 70.8 to 56.6% between the late vegetative and early heading harvest stages, and from 60.2 to 52.1% by sheep. For switchgrass, no consistent differences due to cultivar or location were noted. Dry matter and NDF digestibilities of the hays by beef cows (means of 60.2 and 63.9%) were higher (P<.05) than by sheep (means of 53.2 and 55.2%). Mean apparent protein digestibilities by cattle and sheep were not different (52.5 vs 52.4%). Ad libitum dry matter intake, in g/kg body weight (BW).75, was higher (P<.001) by cows than by sheep, with mean values of 92.3 vs 67.8 g, respectively; species differences were not significant at the BW.9power. Intake decreased with stage of maturity, with no effects (P>.05) of cultivar or location. Intake was associated with DMD percentage in a linear fashion for both cattle and sheep, with correlation coefficients of .80 and .62, respectively. Cattle showed significant positive retentions of Ca, P and Mg from hay at the late vegetative harvest stage, with slightly negative values for Ca and P at later stages. Sheep remained in positive balance of P and Mg at all harvest stages, with negative Ca retention at the earlier cutting dates. Cultivar effects were noted (P<.05) in the apparent retention of Mg and P by sheep.

Alfalfa treated with four levels (0, 112, 224, 448 kg Mg/ha) of kieserite (MgSO4.H2O) fertilizer was harvested in first and regrowth cuttings in three years following initial application, and fed in digestibility, intake and mineral balance trials to growing lambs. Fertilization markedly increased the concentration of magnesium (from .20 to .32% in the 0 and 448 Mg/ha treatments, respectively, over all cuttings), with lesser effects on sulfur concentration (from .21 to .24%), and no effect on concentration of other minerals measured. Concentration increases declined with time after application. Over all trials with ad libitumfeeding, magnesium fertilization had no effect on apparent absorption (AA) or availability of magnesium but increased magnesium retention (from .39 to .74 g/day at the 0 and 448 kg Mg/ha levels, respectively). Retention was found to be a curvilinear function of magnesium intake. Fertilization increased the AA of sulfur, had no effect on AA of calcium, phosphorus, potassium and nitrogen, and did not affect retention of calcium, phosphorus or nitrogen. In two trials in which regrowth alfalfa was fed at both ad libitumand restricted levels, lower dry matter intake resulted in an increased AA of magnesium, calcium, sulfur, potassium and nitrogen, and a decreased retention of magnesium, calcium, phosphorus and nitrogen. Level of kieserite fertilization had no effect on dry matter digestibility of the alfalfa, but intake was increased at the highest level (448 kg Mg/ha) of fertilization in the first 2 years after fertilizer application, with no effect in the third year. The increase in intake over the 0 treatment averaged 8.8 and 11.7% in the first and second years, respectively, with increases in individual cuttings ranging from 3.1 to 18.9%. Intake effects may have resulted, in part, from lower levels of cell-walls noted in alfalfa fertilized at higher levels of kieserite.

Feeding trials were conducted with 428 forages in three forage classes (C3grasses, legumes, C4grasses) fed ad libitum to sheep and with 170 forages fed to cattle over a 20-yr period. Of this total, 153 forages were fed concurrently to sheep and cattle. Where the same forages were fed, mean dry matter digestibility (DMD) and dry matter intake (DMI) were lower (P< .01) for sheep than for cattle, with significant effects of forage class. With the main population of forages, the regression of DMI on DMD was positive and curvilinear (P< .01) for sheep, with no effect of forage class, and positive and linear (P< .0001) for cattle, with a significant effect of class. For all forages, correlations between DMI and neutral detergent fiber (NDF) concentration were −.57 for sheep and −.41 for cattle; regressions differed (P< .05) with class and animal species. Correlations of DMD with NDF and acid detergent fiber (ADF) concentrations were −.45 and −.59 (P< .01), respectively, for sheep, and −.32 and −.39 (P< .01) for cattle; again, regressions differed significantly with class and animal species. Within forage class, regressions of DMD and DMI on fiber components generally were linear. Intake of NDF (NDFI) was related to NDF percentage for all forages by a quadratic regression, with significant differences due to animal species and forage class. Results indicate that relationships between DMD, DMI and fiber fractions differ between forage classes and animal species, that C4grasses are consumed at levels higher than would be expected from their DMD and fiber concentrations and that ruminants increase NDFI in response to higher NDF concentrations in the forage.

Experiments described were conducted to define thyroid abnormalities observed in lambs from ewes grazing orchardgrass fertilized at various levels of nitrogen (N) fertilizer or N plus trace elements. Four fertilizer treatments (56kg N/ha; 168 kg N/ha; 504 kg N/ha; 504kg N/ha + Co, Cu, Mo, Zn and S) were applied to replicated hay and pasture plots of Potomac orchardgrass. Seventy-two western ewe lambs were allocated randomly to fertilizer treatment groups and maintained on pasture and hay from 1967 to 1971. In autumn, 1970, one half of the ewes on each fertilizer treatment received supplemental iodine.Forage iodine concentrations indicated marginal deficiency conditions. The N fertilization level had no effect on iodine concentrations of herbage or hay.Serum thyroxine levels of ewes were not affected by fertilizer treatment or by iodine supplementation. 131I uptake trials with ewes in the autumn and winter of 1970 indicated a greater uptake by unsupplemented ewes than by iodine-supplemented ewes. Histological examination of ewe thyroid glands in 1971 revealed hypertrophy and hyperplasia of the follicular epithelium.Gross thyroid enlargement in newborn lambs was observed in spring, 1969, but not in subsequent years. In 1968, thyroid weights and follicular cell heights from slaughtered lambs, and palpation data from lambs remaining with their dams, suggested that goiter was most severe and most prevalent on high N fertilizer treatments. In 1969 and 1970 there was no apparent relationship between level of N fertilization and the occurrence of lamb thyroid dysfunction.

The data obtained in this study indicate that, in general, nitrogen fertilized orchardgrass in the form of pasture or hay provided an adequate source of most nutrients for a breeding flock of ewes over an extended period of time. A requirement for supplemental P was evident across all treatments after 1 year, although P levels in the forage were adequate by N.R.C. standards. Nitrogen and available energy concentrations in the herbage and hay were apparently adequate, with the exception of 1 year in which the feeding of a poor quality, late-cut hay during the latter part of pregnancy resulted in impaired reproductive performance in ewes and adverse effects on the health and growth of lambs on the low- and medium-N fertilization treatments.Increasing increments of N fertilizer, and the incorporation of micro-elements at a high level of N, had certain specific effects on metabolism and performance of sheep. In the first year, a higher incidence of thyroid abnormalities was noted in lambs born from ewes on the high N treatments. Although ewes on the high N and high N + micro-element treatments maintained higher body weights during pregnancy, birth weight of lambs born from ewes on these treatments tended to be lower. High levels of N fertilization depressed the intake of herbage in spring, but little effect was noted on body weight of the ewes during the spring to autumn grazing season.

The effect of different levels and sources of nitrogen fertilizer on the composition, intake, digestibility and palatability of orchardgrass was determined in hay feeding trials with sheep and rabbits and in a fall grazing study with sheep. Levels of nitrogen from 0 to 448 kg. per hectare increased protein digestibility by sheep in the first- and second-cut hays, had no effect on dry matter or cellulose digestibility in the first cutting, but increased dry matter and cellulose digestibility in the regrowth hay. Nitrogen applied at 112 kg. per hectare in the form of sodium nitrate, ammonium nitrate, ammonium sulfate, diammonium phosphate or urea, had no effect on the digestibility of dry matter, cellulose or protein in the first-cut hay, but some differences in the aftermath forages were obtained. Neither level nor source of nitrogen affected ad libitumconsumption of the first-cut hay. Levels of intake of hay fertilized with a high level of nitrogen (448 kg. N/ha.) or with ammonium sulfate were lower than those of other treatments in the aftermath orchardgrass. There was a significant tendency for a lower dry matter digestibility of the second-cut hays to be accompanied by higher intake values than were obtained with the first-cut forages.Cafeteria trials with sheep showed that both the level and form of nitrogen fertilizer markedly affected the palatability of the hays. Selection behavior was consistent among sheep and between cuttings. Acceptability of the orchardgrass declined with increasing levels of nitrogen fertilization, and there was evidence for a relationship between palatability and a soluble carbohydrate-nitrogen imbalance in the plant. In both hay cuttings preference rankings for orchardgrass fertilized with different forms of nitrogen were in the order: sodium nitrate, ammonium nitrate, ammonium sulfate, urea and diammonium phosphate. While palatability studies with rabbits showed consistency in feeding behavior between animals and among cuttings, there were definite animal species differences (sheep vs.rabbits). Rabbits consumed relatively more of the non-fertilized orchardgrass than of the fertilized hays and ranked the nitrogen source treatments in the order: ammonium sulfate, urea, sodium nitrate, diammonium phosphate and ammonium nitrate.A fall grazing trial, in which sheep were given free access to plots having all nitrogen treatments, showed highest intakes on herbage fertilized with higher levels of nitrogen. There were no significant differences in amount of herbage harvested from plots treated with different nitrogen sources. Intake of grass from individual treatments could be related to total herbage available and to plant composition. Analysis showed differences in composition of the fall harvested forage from that of the earlier hay cuttings. Under grazing conditions dry matter and lignin content of the herbage were correlated significantly with the feeding preferences of sheep.

Feeding trials were carried out to determine the influence of N. P and K fertilization on the intake, digestibility and palatability of Kentucky 31 tall fescue hay. The fertilized hays were fed to sheep in either a conventional trial, with digestibility determined at the ad libitumlevel, or under a cafeteria system, where the animals had a free choice of the different hays.In the conventional trials level of N fertilizer had a significant effect on protein digestibility in both the first and aftermath cuttings. There were no differences in dry matter or cellulose digestibility between fertilized and control treatments in the first cutting, but a significant depression in digestibility in the non-nitrogen fertilized aftermath hays was noted. Ad libitumintake levels for the fescue hays were not significantly different in either cutting, and intake and NVI values were generally lower than for a standard alfalfa.When the first-cutting hays were offered to sheep on a cafeteria basis, the animals showed a decided, and individual ability to discriminate among treatments. The sheep tended to select either one or two major choices and to maintain this selection pattern fairly consistently over a 40-day period. Individuals differed in their feeding behavior, but as a group the primary selection was for fescue treated with phosphate fertilizer, and the second selection was for fescue fertilized at a low (50 lb.) level of nitrogen. The sheep tended to reject the fescue hays fertilized with medium and high levels of nitrogen. While significant differences in preference patterns or palatability due to fertilizer treatment were obtained, these differences appeared to bear no consistent relationship to intake as determined in the conventional system.An attempt was made to relate intake and palatability values to chemical composition, rates of in vitrofermentation and production of VFA from the forages. Differences in ad libitumintake between the fescues and alfalfa were associated with differences in structural components, more particularly with the cell-wall and lignin fractions. These differences were also reflected in the rates of breakdown of cellulose under in virtoconditions. The phosphate-fertilized fescue hay was degraded at a significantly faster rate during the early stages of fermentation than the other fescue hays. Molar ratios of VFA determined in rumen fluid from sheep in the conventional trials showed no significant changes due to fertilizer treatment, but the acetic:propionic acid ratio in rumen fluid from sheep on a standard alfalfa was markedly lower. Intake and NVI values showed a significant negative correlation with the acetic:propionic acid ratio in rumen fluid.Little explanation can be offered for the observed differences in palatability. Variations in the level of carbohydrate, nitrogen and mineral components of the experimental hays were not related consistently to selection behavior. There was some indication of a sub-optimum level of phosphorus nutrition in the cafeteria animals, but the theory of “nutritional compensation” which is suggested requires further investigation.

A series of trials was carried out to determine the influence of growth phase (first vs. regrowth), stage of maturity, nitrogen fertilization (60 lb. N vs. 240 lb. N) and cutting management (continuous growth vs. interval clipping) on the digestibility of Kentucky bluegrass clipped and fed in the fresh form to sheep. Concurrent laboratory trials were performed to determine the feasibility of predicting digestibility coefficients by means of in vitrotechniques, and to examine the influence of method of preparation (as fresh, freeze-dried or oven-dried grass) of the sample and the source of rumen fluid inoculum (from grass or hay-fed sheep) on the in vivo-in vitrorelationship.Significant differences in both animal and in vitrodigestibility coefficients were obtained due to pasture treatment effects, and there were also significant differences in in vitrodigestibility caused by method of preparation of the grass and sources of inoculum. The correlations between in vivodry matter and cellulose digestibility and the in vitrodry matter or cellulose digestibility of either fresh, freeze-dried or oven-dried grass, using either grass or hay inocula, were found to be highly significant. This indicates that any combination of preparation and inoculum might justifiably be used in the prediction of animal digestibility coefficients of dry matter or energy. However, analysis of the data suggested that several of the variable factors examined might significantly affect the in vivo-in vitrodigestibility relationship. Protein digestibility in vivowas found to be as highly related to protein content of the forage as to any measure of in vitroprotein digestion.Analysis of volatile fatty acid distribution in the rumen or in in vitrofermentation mixtures indicated that (1) molar proportions of acids in the rumen of grass-fed sheep differed from those in sheep maintained on hay, containing relatively less acetic and more propionic acid, (2) acetic acid increased and propionic acid decreased in the rumen contents with increasing maturity of the herbage, (3) vegetative growth in August and September produced relatively less propionic acid than a comparable growth in May, (4) there was no apparent effect of level of nitrogen fertilization on the distribution of acids in the rumen, (5) molar proportions of volatile fatty acids produced at 36 hr. in vitrowere similar to those found in the rumen fluid of sheep fed the same substrate, although there was a tendency for higher levels of propionic acid to be present in vitro,and (6) method of preparation of the sample did not affect in vitrodistribution of volatile fatty acids; however, source of inoculum was a significant factor.